This invention relates generally to the field of computer systems and, more particularly to a system and method for detecting digital data encoded in a horizontal overscan portion of a video signal.
Ancillary digital data has been transmitted on analog television signals via various methods for several years. This digital data is used today for the purposes of closed-caption displays, interactive television, and commercial distribution of real time data such as stock quotes and weather reports. Various schemes are used to encode digital data onto the signal, each which has advantages and disadvantages. Horizontal overscan data insertion, invented by Microsoft, is a new method of broadcasting ancillary digital data onto NTSC and PAL television signals and has many desirable characteristics which make it superior to other methods such as VBI (vertical blanking insertion) and field luminance modulation (ref. U.S. Pat. No. 4,807,031).
Interactive toys, games, and learning products for the home are particularly useful applications of data broadcast technology. The data broadcast receiver can be coupled to a wireless data transmitter which removes the need for a cable between the interactive device and the ancillary data receiver. This allows a wider variety of devices and in particular allows television interactive educational toys for children to be developed without the hazards of becoming entangled in a cord to the ancillary data receiver.
In order to effectively broadcast the control data in connection with a video signal, several often competing objectives should be attained. First, as noted above, the control data should be temporarily synchronized with the video signal so that the actions of the controlled devices operate in synchronism with the programming information displayed on the television or monitor. Second, the control data should be easily concatenated with a standard video signal for transmission in a variety of broadcast media using standard equipment. Third, the control data should not interfere with the video signal or visibly disrupt the display of the video signal. Fourth, sufficient bandwidth should be provided in the upstream communication link (e.g., a broadcast-level communication link) to fully satisfy the bandwidth requirements of the downstream communication link (e.g., local wireless communication link). In addition, it would be advantageous for additional bandwidth to be available in the upstream communication link for transmitting additional information for other data sinks to provide advertising, subscription, or emergency warning services, such as e-mail, foreign language subtitling, telephone pages, weather warnings, configuration data for a set-top box, and so forth. It would also be advantageous for the bandwidth of the upstream communication link to be adjustable to meet the cost and performance needs of a wide variety of consumers.
As with the downstream wireless communication link, the protocol for the upstream communication link should be addressable so that several wireless controlled devices, as well as other data sinks, may be controlled simultaneously. The protocol should also be error tolerant and accommodate forward compatibility for future wireless controlled devices and other services that may be provided through the broadcast media. All of these attributes should be implemented at a cost that is feasible to deploy in connection with a system that is primarily intended to be a children""s entertainment product.
Conventional horizontal overscan data receivers are presently used in consumer products and toys to receive signals from the controllers. Controllers send signals such as video signals to these receivers so that consumer products and toys can be interactive with consumers. To provide a synchronized video signal, horizontal overscan receivers rely on the presence of a horizontal synchronization pulse in the horizontal previsible overscan region of the video signal. A video data pulse containing encoded horizontal overscan data appears in a fixed time window or horizontal overscan window following the horizontal synchronization pulse. The horizontal overscan receiver expects to see this data in a predetermined time window on a predetermined number of lines of the video image field. Because the expected time window for occurrence of the data pulse is fixed and predetermined, shifting of the data pulse earlier or later than the expected position can cause data errors in existing systems.
Conventional horizontal overscan data receivers are therefore sensitive to a phenomenon known as horizontal picture shift, or horizontal phase shift. Horizontal picture shift occurs when the active video data shifts from its expected horizontal data position. If the active video data shifts to the left or right by more than approximately 400 ns, then active video data is found in the fixed time window or horizontal overscan window where the receiver expects to find horizontal overscan data. Such a shift in the active video signal corrupts the video data, thus affecting the quality and content of the received data signal.
A variety of different hardware and processing equipment can be introduced into the video stream as it travels from the originating source, through satellite systems, and to the consumer via cable. Each type or brand of video processing equipment introduces a different amount of distortion into the fixed time window or horizontal overscan window. This distortion varies the amount of horizontal picture shift experienced by the horizontal overscan data receiver. For example, two different amplifiers connected to the same cable broadcast system will introduce different amounts of distortion into the video signal. Thus, each amplifier will create a varying amount of horizontal picture shift upon the video signal.
Conventional methods for recovering horizontal overscan data encoded in a video signal use a fixed timing window in the area where horizontal overscan data is expected to reside. Typically, a data pulse is expected between 9.2 and 10.6 microseconds after the horizontal reference synchronization point (HREF). If horizontal phase shift causes active video to shift left of the expected data range, then video beginning at 10.2 microseconds (the beginning of the viewable picture area) will shift into the data window and cause decoding errors. Alternatively, if the horizontal phase shift causes video to shift right, then horizontal overscan data will shift out of the expected data window and cause decoding errors. Using conventional methods for recovering horizontal overscan data requires television broadcasters to maintain timing parameters to within +/xe2x88x92100 nanoseconds of the original timing for proper decoding of the horizontal overscan data by a consumer decoder.
Furthermore, devices employed to maintain this timing accuracy are expensive and degrade the video signal slightly. Many broadcasters do not want to invest in expensive pieces of equipment to correct horizontal phase shift.
Thus, there is a need in the art for a system and method that improves the method for data recovery from a video signal encoded with horizontal overscan data.
There is a further need in the art for a system and method that counteracts horizontal picture shift and permits the recovery of horizontal overscan data from an encoded video signal.
Furthermore, there is a need in the art for a system and method that corrects horizontal phase shift and is relatively inexpensive and non-complex.
The present invention meets the needs described above in a system and method for data recovery from a video signal encoded with horizontal overscan data. Furthermore, the present invention provides a system and method for counteracting horizontal picture or phase shift in a video signal. The present invention also provides a system and method that corrects for the presence of horizontal phase shift and is relatively inexpensive and non-complex.
Generally described, the invention is an adaptive timing module with an adaptive timing processor. The adaptive timing module is configured for extracting and decoding digital data encoded in a horizontal overscan portion of a video signal. The adaptive timing module conducts a sweeping operation through a timing search range within a plurality of scan lines over multiple fields of the video signal to detect a horizontal position within the scan lines associated with the digital data. Based on the sweeping operation, the adaptive timing module determines a desired horizontal detection position within the scan lines. The adaptive timing module then detects digital data encoded at the desired horizontal detection position of subsequent fields of the video signal.
More particularly described, the adaptive timing module conducts a sweeping operation through a timing search range within a plurality of scan lines over multiple fields of the video signal by dividing the timing search range into a plurality of equal sub-portions. Each sub-portion of the timing search range is scanned for the presence of a special data sequence within the scan lines associated with the digital data. The adaptive timing module stores the data detected within each sub-portion, and determines a center point or average of the positions of the sub-portions where a valid sequence is detected. The module then determines a desired horizontal detection position within the scan lines by locking onto the center point or average of the sub-portions where a valid sequence is detected.
In another aspect of the invention, the adaptive timing module conducts a sweeping operation through a timing search range between 8.8 and 11.0 microseconds from a horizontal synchronization pulse or a timing signal that indicates the beginning of a scan line. The horizontal position can include a specific data sequence, such as an intelligent signal detect word. (ISDW), that indicates the beginning of a field of digital data. The adaptive timing module then determines a desired horizontal detection position within the scan lines by comparing the observed data sequence to a stored data sequence, such as a stored intelligent signal detect word (ISDW).
In yet another aspect of the invention, the adaptive timing module repeatedly detects digital data encoded at the desired horizontal detection position of subsequent fields of the video signal until a reset condition is enabled. A reset condition includes the elapse of a predetermined length of time, or manually triggering a reset button.
The invention may also be embodied in a display device for recovering data from a video signal divided into frames, wherein each frame comprises a plurality of horizontal scan lines consecutively illuminated on the display device, wherein each scan line comprises a prescan portion comprising a pre-data encoding zone, and wherein the display device scans the prescan portion for the presence of encoded data in the pre-data encoding zone over a plurality of subsequent frames. The display device determines a set of sampling positions within a prescan portion, and sweeps over the set of sampling positions for the presence of encoded data. The display device detects encoded data within the prescan portion.
In another aspect of the display device, the display device determines a center point or average location of the sampling positions. The display device locks onto the center point of the sampling positions, and uses the center point or average location of the sampling positions for recovering subsequent data from the video signal.